An in-wheel drive system means a system that individually drives and brakes wheels, using a motor mounted inside each of the wheels. An in-wheel system operates a motor mounted on each wheel with a power converter. The in-wheel system has the advantage of being able to considerably contribute to improving safety and fuel efficiency of a vehicle, because it can perform posture control and regenerative braking of a vehicle.
In the in-wheel drive system, however, since a complicated planetary gear is disposed inside a hub bearing, a hub case is necessarily disposed outside the planetary gear to drive wheels and support loads. As a result, there is a problem in that it is required to manufacture a specific hub to use the in-wheel drive system and the in-wheel drive system is not compatible for the existing wheels.
Since secondary reduction is performed by the planetary gear, the capacity of the planetary gear needs to be increased in order to increase torque. However, because it is required to design the width, outer diameter, and the like of the planetary gear largely in order to increase the capacity of the planetary gear, the manufacturing cost increases.
A wheel assembly with an in-wheel motor has been disclosed in Korean Patent No. 10-1080664 (published on Nov. 8, 2011), where the direction of the helix angle, that is, the torsion angle of a counter gear at the left wheel is opposite to the direction of the torsion angle of the counter gear at the right wheel, while the direction of the torsion angle of the planetary gear at the left wheel is the same as the direction of the torsion angle of the planetary gear at the right wheel.
However, in the in-wheel drive assembly having this configuration, the counter gear at the left wheel and the counter gear at the right wheel are different parts with the directions of the torsion angles opposite to each other, resulting in increase in the number of gears.